HYGEOS support forum

Hi François,

As most of ocean color bands are usually saturated in the coastal turbid waters, I would like to retrieve the rhow at the MODIS land bands (i.e., 645nm, 859nm, 459nm, and 555nm) from Polymer package; however, I do not know how to use it? Wondering whether the polymer can work for these land bands?

Regards,
Zheegang

Hi Zheegang,

I understand that you would like to get the water reflectance at MODIS bands that don't saturate. However I don't think you will be able to do it properly. Let me explain.
It is indeed possible to adjust the bands provided by Polymer. This is done via the argument bands_rw to the function run_atm_corr, for example run_atm_corr(..., bands_rw=[412,443,469,488,531,547,555,645,667,678,748,859,869]). This will add bands to Polymer output, without changing the bands used for atmospheric correction.
However, this will not work for MODIS currently, because the land bands configuration is missing from some variables (self.calib in polymer/params.py, tau_r_seadas_modis in polymer/leve1_nasa.py). This would be fairly easy to fix, but there is another reason why you would not get good results. Polymer relies on many bands to perform atmospheric correction (see parameters bands_corr and bands_oc). If some bands saturate, the results will not be correct because the atmospheric signal can not be estimated properly. You would have to use only non-saturating bands, which would require a major change in the spectral configuration, and would probably not work.
I hope this helps.
Cheers,
François